1. Field of the Invention
The present invention relates to a vibration wave motor which drives a movable member by a travelling vibration wave on a vibration member, and more particularly to a structure of a vibration absorption member thereof.
2. Related Background Art
A known example of a vibration wave motor which drives a movable member by a travelling vibration wave is explained with reference to FIG. 1, which shows an exploded view of elements of a vibration wave motor. A vibration absorption member 104, a metal ring-shaped vibration member 102 having electrostrictive elements 103 which serve as electro-mechanical transducers bonded on a surface thereof facing the absorption member 104, and a movable member 101 are fitted, in this order, in a center cylinder 105a of a base fixed member 105. The fixed member 105, absorption member 104, electrostrictive elements 103 and vibration member 102 are arranged not to permit mutual rotation. The movable member 101 is press-contacted to the vibration member 102 by its weight or biasing means (not shown) to maintain the integrity of the motor structure.
A group of electrostrictive elements 103a which form a phase A which is one of the vibration phases arranged at a pitch of one-half of a wavelength .lambda. of the vibration wave, and a group of electrostrictive elements 103b which form another phase B are also arranged at a pitch of .lambda./2. The electrostrictive elements 103a (or 103b) may be a single element instead of a plurlity of elements and the single element may be polarized at the above pitch. The electrostrictive elements 103a and 103b are arranged to have a phase difference of (n.sub.o +1/4).lambda. (where n.sub.o =0, 1, 2, 3,...). A lead wire is connected to each electrostrictive element 103a on the side facing the absorption member 104, a lead wire 111b is connected to each electrostrictive element 103b, and those lead wires are connected to an A.C. power supply (not shown) and a 90.degree. phase shifter (not shown). A lead wire lllc is connected to the metal vibration member 102 and also to the A.C. power supply.
A friction area 101a of the vibration member 101 is made of hardened rubber to enhance a friction force and reduce abrasion, and it is press-contacted to the vibration member 102.
In the vibration wave motor thus constructed, when an A.C. voltage V.sub.o .multidot.sin wt is applied to one group of electrostrictive elements and an A.C. voltage V.sub.o .multidot.cos wt is applied to the other group of electrostrictive elements, the A.C. voltages which are of opposite polarities between adjacent electrostrictive elements and have a phase difference of 90.degree. between the groups are applied to the respective electrostrictive elements and they vibrate. The vibration is propagated so that the vibration member 102 makes a bending vibration in accordance with the pitch arrangement of the electrostrictive elements 103. When the vibration member projects at every other position corresponding to the electrostrictive element, it retracts at another group of every other position. Since one group of the electrostrictive elements are arranged with 1/4/.lambda. shift with respect to the other group of the electrostrictive elements, the bending vibration travels. While the A.C voltage is applied, the vibration is sequentially excited and it travels over the vibration member 102 as the travelling bending vibration wave.
In such a vibration wave motor, the lead wire through which the voltage is applied to the electrostrictive element 103 is directly soldered to the electrostrictive element 103. Accordingly its, mass productivity is low and the solder may be readily peeled off due to the vibration. Depending on the amount of solder deposited, the vibration frequency changes, and the electrostrictive elements are deteriorated by the heat of soldering. In the Japanese Laid-Open Patent Application No. 96883/1984, it is disclosed that an electrical conductive rubber is used as not only a vibration absorbing member but also an electric power supply member for supplying the power to the electro-strictive element group. However, in the disclosed technique, the diameter of the ring-shaped vibration absorption member is equal to or larger than the diameter of the ring-shaped vibration member or electrostrictive elements. In this construction, the vibration of the vibration member which drives the movable member is not efficiently transmitted to the movable member 102.
When the vibration member is ring-shaped, the vibration amplitude of the travelling vibration wave generated on the vibration member tends to be larger on an outer diameter than on an inner diameter, and when the vibration absorption member having the same diameter as the vibration member is used, the large vibration generated on the outer diameter is absorbed. Thus, the vibration which efficiently drives the movable member is absorbed by the vibration absorption member and the drive efficiency is lowered.